The structure-function relationships of oligomeric proteins that function in higher levels of molecular organization are being investigated by biophysical techniques. Present work on two such supramolecular assemblages relies primarily on information available from x-ray diffraction electron microscopy. The pyruvate dehydrogenase complex serves as a model for multienzyme complexes. It occupies a key regulatory position in metabolism and yet there is much still unknown about its mode of action. We have crystallized all component enzymes of the complex although much work remains to be able to reproducibly obtain x-ray diffraction quality crystals. Current efforts are concentrated on the dihydrolipoyl transacetylase core and the flavo-protein components. We have large single crystals of the photoreceptor C-phycoyanin. Studies are in progress to determine more detailed information on the size, shape and symmetry of its aggregates and to locate heavy atom derivatives to analyze its molecular structure.